Rapid Recovery in Plateau-Phase Mammalian Cells

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Abstract
Rapid split-dose and rapid single-dose recovery was examined in 2 rodent cell lines: hamster lung fibroblasts (V-79) and contact-inhibited mouse embryo fibroblasts (10T1/2). Cell turnover in density-inhibited plateau-phase 10T1/2 cell cultures was very low compared with V-79 cells. Plateau cultures were exposed to 60Co .gamma. rays at 85-90 rad/s; 0-90 min of incubation at 37.degree. C was allowed between 2 exposures or following a single exposure before subculture at low density. A rapid phase of recovery occurred in plateau-phase 10T1/2 cell cultures occurring within 4 to 10 min after irradiation. Little recovery occurred during this time in the V-79 cell line. Rapid recovery was not observed in either cell line following irradiation during exponential growth. When plateau-phase 10T1/2 cells were irradiated with a dose of 1100 rad given as two 550-rad doses with exposures separated by 10 min, survival was 5 times better than following a single 1100 rad dose. When 10 min elapsed after a single dose before subculture, a 2-fold enhancement in survival occurred. This rapid recovery was probably an additive effect of split-dose and potentially lethal demage repair. With rapid split-dose recovery little further enhancement in survival occurred when cells were placed under conditions favoring recovery of additional potentially lethal damage.

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